7.2 Coupling and Uncoupling (continued)

Uncoupling Twin Trailers

Uncouple rear trailer:

Lower landing gear of second semitrailer enough to remove some weight from dolly.

Close air shut-offs at rear of first semitrailer (and on dolly if so equipped).

Disconnect all dolly air and electric lines and secure them.

Release dolly brakes.

Release converter dolly fifth wheel latch.

Slowly pull tractor, first semi-trailer and dolly forward to pull dolly out from under rear semi-trailer.

Uncouple converter dolly:

Lower dolly landing gear.

Disconnect safety chains.

Apply converter gear spring brakes or chock wheels.

Release pintle hook on first semitrailer.

Slowly pull clear of dolly.

Caution: Never unlock the pintle hook with the dolly still under the rear trailer. The dolly tow bar may fly up, possibly causing injury and making it very difficult to re-couple.

Coupling and Uncoupling Triple Trailers

Couple second and third trailers:

Couple second and third trailers using the method for coupling doubles.

Uncouple tractor and pull away from second and third trailers.

Couple tractor/first semitrailer to second/third trailers:

Couple tractor to first trailer. Use the method described for coupling tractor semitrailers.

Move converter dolly into position and couple first trailer to second trailer using the method for coupling doubles. Triples rig is now complete.

Uncouple triple-trailer rig:

Uncouple third trailer by pulling the dolly out, then unhitching the dolly using the method for uncoupling doubles.

Uncouple remainder of rig as you would any double-bottom rig using the method already described.

Coupling and Uncoupling Other Combinations

The methods described thus far apply to the more common tractor-trailer combinations. However, there are other ways of coupling and uncoupling the many types of truck-trailer and tractor-trailer combinations in use. There are too many to cover in this manual. Learn the correct way to couple the vehicle(s) you will drive according to the manufacturer and/or owner.

Pay special attention to this statement as it shows up often on the written exam. Remember, you should never unlock the pintle hook with the dolly still under the rear trailer.

Doubles:

Refers to pulling two trailers at the same time, otherwise known as "pups" or "pup trailers" because they're only about 28 feet long. However there are some states that allow doubles that are each 48 feet in length.

Review Questions - Click On The Picture To Begin...

Should you pull a dolly out from under a trailer before you disconnect it from the trailer in front?

Yes, that way you can use the truck and first trailer to pull the dolly away from the rear trailer

No, the dolly should be removed after all trailers have been dropped to avoid damaging the trailer or dolly

No, you should never leave the rear trailer without a dolly attached to it

Removing the dolly before disconnecting is simply personal preference and it doesn't matter much either way

Quote From The CDL Manual:

Uncouple rear trailer:

Park in a straight line on firm level ground.

Apply parking brakes so rig will not move.

Chock wheels of second trailer if it does not have spring brakes.

Lower landing gear of second semitrailer enough to remove some weight from-dolly.

Close air shut-offs at rear of first semitrailer (and on dolly if so equipped).

Disconnect all dolly air and electric lines and secure them.

Release dolly brakes.

Release converter dolly fifth wheel latch.

Slowly pull tractor, first semi-trailer and dolly forward to pull dolly out from under rear semi-trailer.

Next

Should you unlock the pintle hook with the dolly still under the rear trailer?

Yes, the pintle hook should always be unlocked while still under the rear trailer

None of these answers are correct

Unlocking the pintle while under the rear trailer is a matter of personal choice

No, the dolly tow bar may fly up, possibly causing injury and making it very difficult to re-couple

Quote From The CDL Manual:

Caution: Never unlock the pintle hook with the dolly still under the rear trailer. The dolly tow bar may fly up, possibly causing injury and making it very difficult to re-couple.

Prev

Next

Which of these steps for uncoupling the converter dolly is correct?

Release converter gear spring brakes

Quickly pull clear of the dolly

Lock the pintle hook on first semitrailer

Disconnect safety chains

Quote From The CDL Manual:

Uncouple converter dolly:

Lower dolly landing gear

Disconnect safety chains.

Apply converter gear spring brakes or chock wheels.

Release pintle hook on first semitrailer.

Slowly pull clear of dolly.

Prev

Next

Which of these steps about uncoupling the rear trailer is incorrect?

Release dolly brakes

Release converter dolly fifth wheel latch.

Park in a "half circle" on firm level ground

Close air shut-offs at rear of first semitrailer (and on dolly if so equipped)

Quote From The CDL Manual:

Uncouple rear trailer:

Park in a straight line on firm level ground.

Apply parking brakes so rig will not move.

Chock wheels of second trailer if it does not have spring brakes.

Lower landing gear of second semitrailer enough to remove some weight from dolly.

Close air shut-offs at rear of first semitrailer (and on dolly if so equipped).

Disconnect all dolly air and electric lines and secure them.

Release dolly brakes.

Release converter dolly fifth wheel latch.

Slowly pull tractor, first semi-trailer and dolly forward to pull dolly out from under rear semi-trailer.

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